Update banner to point to OTel Day (#4251)

Author: cartermp

layouts/partials/banner.md

@@ -3,8 +3,8 @@
 
 <div class="o-banner">
 
-<i class="fas fa-bullhorn"></i> Don't forget to submit to
-[**OTel Community Day CFP** by April 1st](https://sessionize.com/OTel-Community-Day/)!
+<i class="fas fa-bullhorn"></i> Join us for 
+[**OTel Community Day** on June 25th](https://sessionize.com/OTel-Community-Day/)!
 
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